Here's a crazy idea for a power source. How about running a Stirling engine between the Venus atmosphere and a block of frozen water? As the water warms, melts, and evaporates, it could provide a heat sink. As the steam heats up, the engine would be less efficient, but the steam itself could power a piston or rotate the generator once its pressure is significantly higher than the exterior; steam at Venus temps should easily be 200+ bars (if allowed past planetary protection).

A kg of gasoline, as a comparison, has about 44 MJ/kg. Now granted, you probably wouldn't get very high efficiency, and the whole time your cold area is going to get heat leaking in, but it is an interesting thought exercise.

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Space Enthusiast Richard Hendricks --"The engineers, as usual, made a tremendous fuss. Again as usual, they did the job in half the time they had dismissed as being absolutely impossible." --Rescue Party, Arthur C ClarkeMother Nature is the final inspector of all quality.

I'm a little puzzled by that with as much research as has gone into the four Mars rovers but I'm sure there is a more detailed reason.

Think about the surface conditions on Mars. Chilly, dry, but with electrical heaters 'normal' terrestrial electronics and electro-mechanics work ok

That simply isn't true on Venus. I doubt anything of the mobility system of MER would work on Venus. It's just too different.

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A mission I'm quite interested in is a flying drone observer sent to Mars. I can't find the name of the proposal but I was puzzled at the time that they claimed it would be powered by batteries and only last a couple of hours.

Batteries for the electronics, a small rocket engine for the

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Meanwhile the Solar Impulse team were releasing news about their first trip around the globe with a successful trip through a full night.

Aeronautics on Mars and Earth are very different. Solar Impulse used solar power ( lots of power at Earth ) and a very very efficient airframe

On Mars - the solar power is about half that on Earth ( so already, you're fighting a losing battle ). PLUS - you need an airframe as light and efficient as Solar Impulse just to get off the ground at all, because the air density is so very thin on Mars you have to have an astonishingly efficient airframe travelling at high speed just to generate enough lift to get off the ground.

Solar powered airplanes on Mars are an engineering challenge far far over and above Solar Impuls, and might not even be possible with anything on the engineers shopping list of today.

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What better way to take a lot of data quickly over a vast area than from an aerial vehicle. Among other things, it would allow study of Olympus Mons and Valles Marineris, two very interesting geologic locations that are unlikely to be explored by rovers.

How about orbiters? You can take a lot of data, quickly, again and again, mapping those sites That's what killed Ares really, CRISM on MRO producing 6m/pixel hyperspectril Vis-IR mapping spectrometer data, HiRISE producing 25cm/pixel imagery etc etc.

I remember pre-MRO orbit insertion, there was some talk that 25cm wouldn't be achievable due to atmospheric effects. Now that has been put to rest, are there any thoughts on how high resolution we could get from an orbiter? 5 cm or maybe even less? Would be crazy to read the sundials on the MERs from space!

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Space Enthusiast Richard Hendricks --"The engineers, as usual, made a tremendous fuss. Again as usual, they did the job in half the time they had dismissed as being absolutely impossible." --Rescue Party, Arthur C ClarkeMother Nature is the final inspector of all quality.

Umm - no. Even if the KH11's still existed ( which they don't - I think they've all reentered ) - they have nothing for which a very significant propulsive upper stage (>10tons to Mars...that's one hell of an ask for any existing booster) could dock on to, they're not designed for the thermal environment for a cruise to Mars, they don't have solar arrays qualified for operation at Mars, and they're not equipped with communications equipment to talk to Earth from Mars either.

Obviously, ZLD was joking slightly. But the question does remain, would larger-than-MRO-HiRISE telescopes be worthwhile in Mars orbits, or would they lose out due to atmospheric distortion? It looks like the equation for a diffraction limited telescope is pretty linear at this size, with doubling the resolution requiring double the mirror diameter. So getting 5cm resolution would require an ~ 3m telescope. Getting that into Mars orbit is left as an exercise for the reader. But a 1m or 1.5m telescope could be reasonably sent to Mars, giving 8cm resolution.

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Space Enthusiast Richard Hendricks --"The engineers, as usual, made a tremendous fuss. Again as usual, they did the job in half the time they had dismissed as being absolutely impossible." --Rescue Party, Arthur C ClarkeMother Nature is the final inspector of all quality.

A linked array of small telescopes could push the limit down. Add a laser and 'adaptive optics' applied to the array and you take care of the slight atmosphere. I doubt if there is a theoretical limit to resolution of the martian suface that can be obtained from orbit.

Vote for your favorite Decadal Survey missions in a poll at my blog, Futureplanets. Early votes (before I could post the announcement) had some surprises for me. Should be fun.

In two months, we can compare our choices with those made by the voters that really counted.

Me as well; I actually voted for the third most-popular mission purely because I think that Uranus & Neptune have not received nearly enough attention. (Won't debate the scientific merits of that viewpoint, but obviously there is always knowledge to be gained regardless of the target.)

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A few will take this knowledge and use this power of a dream realized as a force for change, an impetus for further discovery to make less ancient dreams real.

I can't see that anyone else has reported this: ESA have today announced the four shortlisted mission candidates for the M3 medium-class mission for launch around 2022.

Marco Polo, which narrowly lost out in the competition for consideration for an earlier M1 or M2 mission slot, is through again. Also of planetary science interest is exoplanet-characterization mission EChO. It doesn't look like ESA are going to provide a full list of the 47 submitted proposals, but I understand that there were many planetary proposals submitted.

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